1. Field of the Invention
An aspect of the present invention relates to an organic light emitting display and a driving method thereof, and more particularly to an organic light emitting display capable of displaying an image having uniform luminance regardless of the degradation of organic light emitting diodes, and a driving method thereof.
2. Description of the Related Art
In recent years, there have been developed a variety of flat panel displays having a reduced weight and volume compared to the cathode ray tube (CRT). The flat panel displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), organic light emitting displays (OLED), etc.
Among the flat panel displays, the organic light emitting display uses an organic light emitting diode to display an image. The organic light emitting diode generates light by recombining electrons and holes. Such an organic light emitting display is advantageous in that it has a rapid response time and is driven by a small amount of power.
FIG. 1 is a circuit diagram showing a pixel of a conventional organic light emitting display. Referring to FIG. 1, the pixel 4 of the conventional organic light emitting display includes an organic light emitting diode (OLED) and a pixel circuit 2 coupled to a data line (Dm) and a scan line (Sn) to control an organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is coupled to the pixel circuit 2, and a cathode electrode is coupled to a second power source (ELVSS). Such an organic light emitting diode (OLED) generates the light having a predetermined luminance using an electric current supplied from the pixel circuit 2. When a scan signal is supplied to the scan line (Sn), the pixel circuit 2 controls the capacity of current supplied to the organic light emitting diode (OLED) to correspond to a data signal supplied to the data line (Dm).
For this purpose, the pixel circuit 2 includes first and second transistors (M1 and M2) and a storage capacitor (Cst). Here, the second transistor (M2) is coupled between a first power source (ELVDD) and the organic light emitting diode (OLED), and the first transistor (M1) is coupled between the second transistor (M2), the data line (Dm) and the scan line (Sn). Also, the storage capacitor (Cst) is coupled between a gate electrode of the second transistor (M2) and a first electrode.
More particularly, the gate electrode of the first transistor (M1) is coupled to the scan line (Sn), and the first electrode is coupled to the data line (Dm). A second electrode of the first transistor (M1) is coupled to one side terminal of the storage capacitor (Cst).
Here, the first electrode is set to one of a source electrode and a drain electrode, and the second electrode is set to the other electrode that is different from the first electrode. For example, if the first electrode is set to a source electrode, the second electrode is set to a drain electrode. The first transistor (M1) coupled to the scan line (Sn) and the data line (Dm) is turned on when a scan signal is supplied from the scan line (Sn), and supplies a data signal, supplied from the data line (Dm), to the storage capacitor (Cst). At this time, the storage capacitor (Cst) is charged with a voltage corresponding to the data signal.
A gate electrode of the second transistor (M2) is coupled to one side terminal of the storage capacitor (Cst), and the first electrode of the second transistor (M2) is coupled to the other side terminal of the storage capacitor (Cst) and to the first power source (ELVDD). The second electrode of the second transistor (M2) is coupled to an anode electrode of the organic light emitting diode (OLED).
Such a second transistor (M2) controls the capacity of current that flows from the first power source (ELVDD) to the second power source (ELVSS) via the organic light emitting diode (OLED) to correspond to the voltage value stored in the storage capacitor (Cst). At this time, the organic light emitting diode (OLED) generates light corresponding to the current capacity supplied from the second transistor (M2).
However, the conventional organic light emitting display is disadvantageous in that it is impossible to display an image having a desired luminance due to the efficiency change caused by the degradation of the organic light emitting diode (OLED).
The organic light emitting diode (OLED) degrades with time, and therefore light with gradually decreasing luminance is generated in response to the same data signal.